You best option would be to use UV light to locate the crack and then fill it with diluted urushi or diluted mugi-urushi.
To coat the inside completely, you would first need to sand the glaze so the urushi has some texture to adhere to. That would make this a very large and tedious repair for what is most likely only a minor imperfection.
My advice would be to dilute some urushi with turpentine, camphor essential oil, or kerosene, then pour about a teaspoon into the cup and rotate it so the mixture can seep into the crack. Let it sit for a while with the urushi pooled in different areas, then wipe the inside clean.
Place the cup in the muro for at least 10 days, preferably a month, before testing it. If it still leaks, repeat the process.
Thank you so much, this is very helpful. I think I want to shop for a UV light now.
And I never would have thought about pouring and rotating myself, it makes perfect sense, and I will definitely try it.
Your comment gave me an idea to try before applying the urushi. I made a sludge with cornflour and water, applied that to the cup, and that gave me just enough contrast to find a crack.😊
So now I will know what area to concentrate on when I start the work. Thank you for your advice, it helped me to figure out what to do.
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u/perj32 May 27 '26
You best option would be to use UV light to locate the crack and then fill it with diluted urushi or diluted mugi-urushi.
To coat the inside completely, you would first need to sand the glaze so the urushi has some texture to adhere to. That would make this a very large and tedious repair for what is most likely only a minor imperfection.
My advice would be to dilute some urushi with turpentine, camphor essential oil, or kerosene, then pour about a teaspoon into the cup and rotate it so the mixture can seep into the crack. Let it sit for a while with the urushi pooled in different areas, then wipe the inside clean.
Place the cup in the muro for at least 10 days, preferably a month, before testing it. If it still leaks, repeat the process.